This invention relates generally to the design and construction of shrouds for bladed axial flow fans. More particularly, the invention relates to a shroud for the fan that circulates air through the enclosure that houses the compressor and outside heat exchanger in what are known in the industry as "split" air conditioning (including heat pump) systems.
Efficiency and reduction of radiated noise levels are objectives in the design and construction of all the components of an air conditioning system. Air flow noise is a major contributor to the total radiated noise produced by a number of components of the typical air conditioning system. One such component is the fan that moves air through the outside enclosure and over the refrigerant-to-air heat exchanger contained in the enclosure.
The proper operation of the air conditioning system requires a certain minimum rate of flow of air across the outside refrigerant-to-air heat exchanger. The total air flow rate through the outside enclosure, and hence over the heat exchanger, is a function of the effective area swept by the fan and the average velocity of the air through the fan. In general, fan radiated noise level increases as the air flow velocity through the fan increases. It is therefore an objective in the design of the outside enclosure to achieve the required air flow through the enclosure while keeping air flow velocity and thus fan radiated noise level at a minimum. To achieve this objective, a designer would first look to increasing fan size. Other design considerations such as minimizing the overall dimensions and cost of the enclosure work against such a simple solution and require that other, more sophisticated measures be taken to improve fan efficiency and thus reduce noise.
Other considerations complicate the designer's problem. To minimize the overall height of the unit, the outside enclosure fan and motor are frequently recessed into the top of the annular space between the coiled refrigerant tubing of the heat exchanger. The designer must configure the fan and its associated shrouding so that there is at least some air flow over the uppermost tubing coils of the heat exchanger so that the effective heat transfer area of the heat exchanger is maintained. Safety, aesthetic and other considerations require that a covering grille be fitted on the top of the unit over the discharge of the fan. Air flow noise from the grille is a contributor to overall radiated noise from the enclosure. This noise, like the noise from the fan itself, can be reduced by reducing the maximum air velocity at the grille.